Melt butter with oil in large pot over medium-high heat. Add onions and apples; sauté until soft and dark brown, about 20 minutes. Add chicken broth, apple juice concentrate, and thyme sprigs. Bring to boil. Reduce heat; season with salt and pepper. Simmer soup, uncovered, 25 minutes. Discard thyme sprigs. Divide among 6 soup bowls.